Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography and etch processes to form circuit components and elements thereon.
Chemical-mechanical polishing (CMP) processes are often used to planarize material layers of semiconductor devices. In many integrated circuit designs, material layers are planarized before depositing subsequent material layers. CMP processes are typically used for global planarization of a semiconductor wafer, and to remove excess material from over certain topographical features, e.g., after an etch process or deposition process, for example. In a CMP process, elevated features of a wafer are selectively removed, e.g., material from high elevation features is removed more rapidly than material at lower elevations, resulting in reduced topography. The process is referred to as “chemical-mechanical polishing” because material is removed from the wafer by mechanical polishing, assisted by chemical action.
It is important for etch processes and CMP processes to have a uniform effect on semiconductor devices during the fabrication process in some designs, so that the various devices formed thereon have uniform electrical parameters. A planar surface is also important in order to achieve depth of focus (DOF) for lithography processes, for example.
Some semiconductor device designs have regions that are densely populated with features and other regions that are absent features or are less densely populated with features. A CMP process may affect the more densely populated regions differently than the less densely populated regions, resulting in an uneven planarization process. For example, less densely populated regions may be planarized more than more densely populated regions. Dishing of material layers may also occur in less densely populated regions, as another example. Uneven planarization and dishing may present problems later in the manufacturing process as subsequent material layers are deposited and processed over the wafer.
Thus, what are needed in the art are improved methods of fabricating semiconductor devices and structures thereof.